Euler/ALE Basics

caeguy

Eulerian/ALE
  
Euler/ALE Basics
  
Eulerian fluids such as air or water are generally modeled using *MAT_NULL and an accompanying equation-of-state (*EOS_. . . ).  
  
For a case where there is only one Eulerian material, I would recommend you use solid element formulation 12 (single material with void) to model the Eulerian material and any empty cells around the Eulerian material into which that material may ultimately be transported[1]. The empty cells (which typically overlay your Lagrangian parts) are identified using *initial_void. All the Eulerian parts (filled or void) should be given material/EOS properties of the Eulerian material. Use hexahedron (brick) elements and hourglass type 1. A reduced hourglass coefficient, e.g., . 001, is recommended if the Eulerian material is a fluid.  
  
For cases where there are multiple Eulerian materials, use solid formulation 11 (multi-material). For this, each Eulerian material must be assigned to a group using *ale_multi-material_group. Each part within a specific group has identical material properties.  
  
Eulerian meshing can be done using one of the following two approaches:
  
The initial mesh conforms to the material. In other words, there are no mixed (or partially filled) cells in the initial configuration. Mesh lines follow the outer contour of each Eulerian part.  
A simple orthogonal mesh may be constructed with no restriction that mesh lines follow the outer contour of each Eulerian part. The volume fraction of initially mixed cells must be prescribed via *initial_volume_fraction. Version 970 has a "geometry" option to *initial_volume_fraction that automates the assignment of initial volume fractions to cells.  
In either approach, there is no requirement that the Lagrangian nodes align with the Eulerian nodes. In your coupling definition (*constrained_lagrange_in_solid), you may have to increase NQUAD if the structural mesh is coarser than the Eulerian mesh (in order to prevent 'leakage' in the coupling). Your Lagrangian segment normals must point toward the Eulerian fluid (note you can reverse the normals using NORM). If you are coupling Lagrangian solids to the Eulerian fluid, you MUST set CTYPE to 5 unless the slave side is identified by segments instead of by part ID. Set MCOUP to 1 in cases where one of the Eulerian materials dominates the loads imparted to the Lagrangian structure, i.e. its density is much higher than the other Eulerian materials. Typically DIREC should be set to 2 when a penalty-based coupling is used.  
  
As an alternative to coupling (*constrained_lagrange_in_solid), you can, in some cases, merge (share) nodes at the interface between a Lagrangian part and an ALE part. The shared nodes will move as Lagrangian nodes. The interior of the ALE mesh must then be smoothed using one or a combination of smoothing algorithms (see *control_ale) and, if the situation warrants, *ale_smoothing constraints.  
  
To view the Eulerian material in LS-POST, use Fcomp > misc > history var#.  
  
The definition of the history variables are as follows:
  
1 = density
  
2 = volume fraction of 1st multi-material group (formulation 11) or single Eulerian material (formulation 12)
  
3 = volume fraction of 2nd multi-material group (formulation 11) etc.  
  
It's sometimes clearer to view isosurfaces of Eulerian history variables rather than fringes (click on the Frin button and choose Isos).  
  
Notes:
  
The command *ale_reference_system(_option) can be utilized in some situations to reduce the spatial extent of the initial Eulerian mesh. This command directs the Eulerian/ALE mesh to move through space in a prescribed manner rather than remaining fixed in space like a pure Eulerian mesh.  
  
jpd 8/2002  
revised 11/5/02  
revised 11/14/02  
revised 1/6/03

ls_dyna

版主呀，能否详细讲解一下：
As an alternative to coupling (*constrained_lagrange_in_solid), you can, in some cases, merge (share) nodes at the interface between a Lagrangian part and an ALE part. The shared nodes will move as Lagrangian nodes. The interior of the ALE mesh must then be smoothed using one or a combination of smoothing algorithms (see *control_ale) and, if the situation warrants, *ale_smoothing constraints.  
  
中这个smooth的详细实现方法，我很需要，可是没有找到详细说明，能否有例题给我一个呢？
谢谢

bq204

谢谢，受教了

smjerik

受教,谢谢